In a rolling mill for steel sheet of plate, it is common to provide at least one shear for subdividing a length of the rolled mill product, e.g. heavy sheet steel or steel plate, into lengths of a selected size after rolling has been completed.
A typical dividing shear for this purpose, e.g. the transverse subdivision of a boiler plate and like heavy milled product, generally includes a transport path (roller conveyor) for the length of the rolled mill product to be subdivided and a shear stand athwart the path for severing the length into sections.
The shear can include a spatially fixed lower blade and a movable upper blade formed as an inclined blade (vertically movable guillotime-type blade) or as a roll-shearing blade.
The inclined edge of the descending movable blade or the rolling movement of the roll-shearing blade, in cutting through the metal, generates a cutting-force component in a transverse direction (i.e. the direction in which cutting progresses across the plate) which is taken up by guide rollers or like lateral supporting elements along the longitudinal edge of the plate opposite to that at which the cutting commences.
In addition, hold-down means, e.g. a clamp immediately upstream of the blades, presses the plate against the fixed lower blade.
In the transverse subdivision of milled products by means of dividing shears of the aforedescribed type, the incoming section of sheet or plate is, on the one hand, guided along the aforementioned rollers or lateral supporting elements and, on the other hand, by the hold-down clamps, is secured in a precisely fixed position.
At the downstream side, however, the blade section which is to be cut off from the length is subjected to force components of the type described because of the passage of the upper blade through the sheet. This force component has a tendency to displace the plate in the region of cutting, transversely to its plane, i.e. in the vertical direction. This displacement is induced by the vertical passage of the blade through the plate and as a result, the downstream side of the plate is generally provided on a so-called rocker whose movement leads the cutting stroke of the upper blade.
In addition, because of the inclination of the cutting edge of the linearly displaceable upper blade or the rolling movement thereof, a cutting force component is applied to the downstream side of the plate, i.e. to the plate section to be severed, which tends to shift the latter in a direction parallel to the cutting line. This tendency is taken up the by aforementioned guide rollers or, more generally, by the lateral-supporting elements.
In addition, however, the cutting action results in a so-called springing or "chewing" pressure between the blade flanks of the upper and lower blades which tends to swing the downstream plate section substantially transversely to the cutting line with a substantially horizontally directed force. This is recognized as a tendency of the cut line to widen from the starting side toward the side at which cutting terminates.
As a result, the cut tends to separate at the starting side and with the progress of the cutting operation in the form of a wedge-gap which converges toward the supported longitudinal edge of the length of plate. The widest portion of this gap is at the longitudinal edge at which the cut commences.
This tendency to rotate the section of plate which is to be severed from the length cannot always be effectively taken up by the guide rollers or like lateral support elements. As a consequence, especially when conventional shears of the aforedescribed type are used and the mill product has a large thickness, as is the case with boiler plate and like thicknesses of steel, the cut may be imprecise and is seldom clean. In other words, the tendency to twist the severed section of the plate in a horizontal plane away from the remainder of the length thereof has a tendency to tear the plate and reduce the cleaness of the cut.